3D Current collectors for Lithium metal anodes: A review on concepts of performance

Lithium metal anodes (LMAs) have the potential to boost cell-level energy densities when coupled with high-capacity cathode materials compared with the ubiquitous graphite electrodes. However, LMAs face several outstanding challenges, including dendritic Li growth, high-volume expansion, and low mechanical strength leading to poor formability for thin and large-format anodes, among others. One approach to address some of these issues is to replace the conventional 2D foils with 3D current collectors (3DCC) which possess high surface areas, open porous structures that are beneficial for increased electrolyte infiltration, faster Li ion transport, and shorter electron transport pathways, all of which can also lower the internal resistance of the cell. This article reviews the theoretical background of the potential influence of 3DCC on the Li plating process, different approaches for manufacturing 3DCCs, and current methodologies for obtaining Li anodes for high-volume manufacturing. For LMAs, the potential benefits of Li-containing 3DCCs are the accommodation of Li volume expansion due to the porous host structure, reduction of local current density due to the higher surface area of the 3D structure, and possibly improvement in the LMA mechanical integrity. Various methods for producing 3DCC structures by the "bottom-up" or the "top-down" methods are described. The synergistic effect of the optimized porous structure (e.g., surface area, pore size & density, tortuosity) of 3DCCs and the "lithiophilic" coatings, providing a wettability of Li, improves cycling performance of LMAs by favoring large-sized and dendrite-free Li deposits. Finally, Li electroplating, evaporation, molten form, and rolling methods have been evaluated for their potential in providing Li metal contained within 3DCCs, each has advantages and shortcomings. Nonetheless, rolling Li on current collectors to produce LMAs is considered the most scalable paradigm due to the room temperature operation conditions and the fact that the wettability of Li is not highly limiting their fabrication.